(1) Field of the Invention
The invention relates to a device to support rudders and trailing edge flaps of aircraft and watercraft with a cover for the gap existing between the rudder and the corresponding fin or wing, respectively, the cover connecting tangentially with the fin and the rudder.
For the sake of simplicity, hereinafter reference will be made only to the support of a rudder in a rudder fin, whereby the entirety of the rudder and the fin shall be designated the steering gear. This is analogous to the support of ailerons and trailing edge of flaps in the wing of an aircraft or a hydrofoil boat, for which the invention is particularly suitable.
(2) Description of the Prior Art
In a known embodiment of such a device, the rudder is rotatingly supported around a stationary axis of the fin. Without an additional device, the gap generated in this manner between the rudder and the fin is penetrated by a flow of air, introducing a large volume of detrimental drag and decreasing the efficiency of the rudder. Due to this known fact, the gap is frequently sealed adhesively by means of a soft, air-tight strip in efficient aircraft. Although this solution has demonstrated advantages, it still represents an unsatisfactory solution of the problem, since the adhesively bonded strip must necessarily form corners and wrinkles whenever the rudder is in motion. Because the length to be covered differs in accordance with the various positions of the rudder, the cover strip must be just tight in the lowest position of the rudder, whereby corners are formed in its external configuration. In the undeflected position, the strip forms wrinkles which are aggravated in the upwardly deflected position. It is also known to arrange the rotational axis of the rudder exactly in the top side of the wing, see DE-PS 424 064. The cover strip is then able to cover the sharp edge generated between the rudder and the fin, without forming large folds. The disadvantage therein, however, consists of the fact that the support, which does not extend over the entire length of the rudder but is restricted to individual locations, protrudes beyond the configuration of the wing. At this location and at the sharp edge prevailing during the deflection of the rudder, a certain amount of detrimental drag is still generated, causing reduced steering efficiency and in watercraft the increased danger of cavitation.
For this reason, another arrangement according to DT-PS 386 926 provides a cover for the rudder gap by means of special metal strips, the strips being supported swingingly in the surface of the fin and pressed elastically onto the rudder, upon which they slide during the deflection of the rudder. In the process, the interfering edges of the arrangement are reduced but not eliminated, while the forces required to move the rudder become excessive due to the sliding friction at forces which are generated. The same is true for the arrangement of FR P 524 814. There, the cover strips are provided with slits which engage with guiding devices mounted on the rudder.
In another aerodynamically and cavitationally favorable arrangement according to DT-PS 386 926, the existence of an external skin of the craft is assumed, the skin passing over on both sides without a slit, into the outer skin of the rudder. During the deflection of the rudder, the entire outer skin of the rudder must then slide on the rudder, again leading to excessive force requirements during steering.
Finally, attempts have been made for decades, particularly in the case of gliders, to design the fins or the top side of the wing, respectively, in an elastic manner and to deform the rear part of the steering gear elastically, whereby a gap would be formed on the bottom side only. All of these solutions have the common characteristic that as the result of the aerial forces and momentum generated at the deformable part of the fin, the elastic top side of the fin must transfer high compressive forces. The top side must therefore be designed to have suitable strength, and this requires strong forces for deformation. For this reason, none of these solutions have been successful to date.
In another known device, the rudder is supported so that the slit may be covered elastically, i.e. without corners and folds, without the need for such covers to be used for the transfer of forces (German application P 21 14 459.2-22). In this solution, the rudder is guided by means of a bearing device so that the cover has the same length s in all positions of the rudder and so that the cover may have an approximately constant curvature over this length. The cross-section of the cover should always approximately represent a circular arc or a straight line of constant length. It is only necessary for the cover to maintain its own configuration, whereby it may be bonded adhesively to the rudder and the fin. With the exception of the forces which retain it in its constant shape, the cover is not required to transfer other forces. It may be very thin and the force needed for its deformation is not substantial.
A movement of the rudder which would satisfy this requirement ideally may be described and expressed very simply by a formula, in which the cover is to pass tangentially into the fin and the rudder and is to have an exactly constant curvature over its length s, which is also constant. For this ideal movement, the so-called instantaneous pole of the motion may be calculated in any position, by means of known methods (see: W. Wunderlich, "Planar Kinematics", Mannheim 1970, pp. 16-19). In this manner, the locus of the instantaneous center (center path curve) and the so-called path curve variation (herpolhode curve) of the ideal motion may be found. These lines indicate that the ideal motion may be described very accurately, but not exactly, by imagining that circular disks having radii of one-third s are connected with both the rudder and the fin, the disks contacting each other in the nondeflected position (zero position) in the center of the cover with their tangent line perpendicular to the cover and rolling upon each other during movement of the rudder. In particular, the instantaneous center of motion for the zero position is located in the center of the cover.
Furthermore, the path of each point of the rudder may be readily calculated during ideal motion; and it is designated the ideal path of the point of the rudder. It does not represent a circular path, just as for example the path of a point of a wheel rolling down a plane does not generate a circular path but a so-called cycloid. One point of the ideal path thus corresponds to the zero position of the rudder and therefore defines the position of the chosen point of the rudder in the zero position, i.e. the nondeflected state of the rudder. In the vicinity of the point the ideal path may be approximated by a curve, having the same tangent and the same curvature at this point, as the ideal path. The tangent is given by a line perpendicular to the connecting line to the instantaneous center, which in the zero position is located in the center of the cover. The curvature k at a point P of a path may be calculated by known methods (see for example: Bronstein-Semendjajew, "Handbook of Mathematics", p. 205). The curvature k is visualized by its reciprocal value, the radius K of curvature. The circle of curvature having the radius R and contacting the path at P, is a second order approximation of the path in the vicinity of P. In case of a sufficiently smooth path, the deviation between the path and the circle of curvature is proportional to the third power of the distance to P. If the chosen point of the rudder is displaced from the end point B of the cover downward by y and by x in the direction of the fin, then the following equation yields the radius of curvature R of the ideal path at the point P, corresponding to the zero position: ##EQU1## The same formula is valid for the relative motion of a point of the fin with respect to the rudder assumed to be at rest. In this case, it is merely necessary to measure y from the end point A of the cover in the direction of the rudder.
A device capable of satisfactorily approximating the ideal motion is described in the German application P 21 14 459.2-22. According to this invention, the rudder is supported by means of a so-called four bar arc so that two points of the rudder move on the circle of curvature of their ideal path as defined hereinabove. However, part of this four bar arc protrudes beyond the elastic cover, so that said cover must be interrupted at these bearing locations. The hole formed in the process is covered by a rubber scoop, which again presents a certain drag. In addition, two bearing points of the four bar arc must be located closely adjacent to each other, which renders the design embodiment of this solution difficult.